From: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
To: Israel Rukshin <israelr@mellanox.com>,
Linux-nvme <linux-nvme@lists.infradead.org>,
Sagi Grimberg <sagi@grimberg.me>, Christoph Hellwig <hch@lst.de>,
James Smart <jsmart2021@gmail.com>,
Keith Busch <kbusch@kernel.org>
Cc: Max Gurtovoy <maxg@mellanox.com>
Subject: Re: [PATCH 3/3] nvmet-loop: Avoid preallocating big SGL for data
Date: Mon, 25 Nov 2019 02:24:52 +0000 [thread overview]
Message-ID: <BYAPR04MB57494D9693539C308A75AF23864A0@BYAPR04MB5749.namprd04.prod.outlook.com> (raw)
In-Reply-To: 1574613512-5943-4-git-send-email-israelr@mellanox.com
Looks good, tested with simple loop setup running ranread
4K I/Os with fio.
Tested-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
On 11/24/2019 08:39 AM, Israel Rukshin wrote:
> nvme_loop_create_io_queues() preallocates a big buffer for the IO SGL based
> on SG_CHUNK_SIZE.
>
> Modern DMA engines are often capable of dealing with very big segments so
> the SG_CHUNK_SIZE is often too big. SG_CHUNK_SIZE results in a static 4KB
> SGL allocation per command.
>
> If a controller has lots of deep queues, preallocation for the sg list can
> consume substantial amounts of memory. For nvmet-loop, nr_hw_queues can be
> 128 and each queue's depth 128. This means the resulting preallocation
> for the data SGL is 128*128*4K = 64MB per controller.
>
> Switch to runtime allocation for SGL for lists longer than 2 entries. This
> is the approach used by NVMe PCI so it should be reasonable for NVMeOF as
> well. Runtime SGL allocation has always been the case for the legacy I/O
> path so this is nothing new.
>
> Signed-off-by: Israel Rukshin<israelr@mellanox.com>
> Reviewed-by: Max Gurtovoy<maxg@mellanox.com>
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next prev parent reply other threads:[~2019-11-25 2:25 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-24 16:38 [PATCH 0/3] nvme: Avoid preallocating big SGL for data Israel Rukshin
2019-11-24 16:38 ` [PATCH 1/3] nvme-rdma: " Israel Rukshin
2019-11-26 16:53 ` Christoph Hellwig
2019-11-24 16:38 ` [PATCH 2/3] nvme-fc: " Israel Rukshin
2019-11-25 17:04 ` James Smart
2019-11-24 16:38 ` [PATCH 3/3] nvmet-loop: " Israel Rukshin
2019-11-25 2:24 ` Chaitanya Kulkarni [this message]
2019-11-26 16:53 ` Christoph Hellwig
2019-11-26 17:40 ` Keith Busch
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